The present invention is a one-component room temperature vulcanizing silicone rubber composition comprising a silanol end-terminated polyorganosiloxane base polymer, an organotriacyloxysilane, a polysiloxane-polyether copolymer as a rheology modifying agent, and a particulate silica. The rheology modifying agent is particularly useful for controlling the viscosity and plateau stress of such silicone rubber compositions.
One-component room temperature vulcanizing silicone rubber (RTV) compositions are well known in the art. Examples of such silicone RTV compositions are described in U.S. Pat. No. 3,035,016, U.S. Pat. No. 3,133,891, and U.S. Pat. No. 3,296,161. These silicone RTV compositions generally consist of a silanol end-terminated polydiorganosiloxane polymer, a silica filler, an organotriacyloxysilane as a cross-linking agent, and a metal salt of a carboxylic acid as a catalyst. The silicone RTV compositions cure to a solid elastic state at room temperature upon exposure to moisture commonly present in the atmosphere. Silicone RTV compositions are very useful in sealing and caulking applications where strong adhesion to various surfaces is important. Such uses of silicone RTV compositions often required that the compositions be placed in cracks and on surfaces having a vertical orientation or positioned overhead, therefore it is important that such compositions have viscosity and slump properties that allow them to be extruded freely into or onto cracks and surfaces and after placement the composition has limited slump.
Silica is used as a primary rheology control agent in many silicone RTV compositions. However silica is often the most expensive component of silicone RTV compositions, and therefore it is desirable to reduce the amount of silica in such compositions while maintaining the desired rheology properties. The present compositions comprise a novel group of polysiloxane-polyether copolymers as rheology modifiers. The degree of polymerization of the polysiloxane segment of the copolymers as well as the size and functionality of the polyether components can be varied within the described ranges to provide for silicone RTV compositions having rheology properties desirable for a particular application. Furthermore, these rheology additives can allow for the reduction of silica levels in silicone RTV compositions while maintaining desired rheology properties.
Wright et al., U.S. Pat. No. 4,261,758, teach a silicone RTV composition with sag-control comprising a silanol end-terminated polydiorganosiloxane polymer, at least 3 parts by weight of a fumed silica and as the sag-control ingredient, from 0.03 to 2 parts by weight of a polyether.
Bluestein, U.S. Pat. No. 4,304,897, teaches a silicone RTV composition having improved flow characteristic consisting of a silanol end-terminated linear polydiorganosiloxane base polymer, a filler, an organotriacyloxysilane cross-linker, a catalyst and a polyorganosiloxane copolymer consisting of a polysiloxane chain and a polyether chain which are linked together through various carboxyl alkyl radicals.